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rkatl
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 06:50
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If N represents the number of digits in X where X = 4^9 X 5 ^ 25
What is the value of N ?



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Professor
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 06:59
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rkatl
If N represents the number of digits in X where X = 4^9 X 5 ^ 25
What is the value of N ?
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good question. i also donot know the best approach to deal with this kind of question.
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Riya05
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 07:20
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One way to look at it:

4^9 * 5^25
==> (4*5)^9 * 5^16
==> 2^9 * 10^9 * 5^16
==> (2*5)^9 * 10^9 * 5^7
==> 10^18 * 5^7
==> 78125 * 10^18
==> 5 digits + 18 digits = 23 digits.

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rkatl
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 07:45
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I don't know the OA. It is a real GMAT question
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BG
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 08:26
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i WILL TRY TO GIVE YOU A HAND HERE.
4^9=2^18 then the stem is equal to( 2^18)*5^25=10^18*5^7.
10^18 has 19 digits and 5^7 has 5 digits. Then the resulting number will have 5 digits from 5^7 and 18 zeros or N is 23
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 08:48
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good approach.. btw, how do you know 5^7 has 5 digits ? Did you just multiplied or is there a trick ?
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If N represents the number of digits in X where X = 4^9 X 5 15 Aug 2006, 10:20
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BG
i WILL TRY TO GIVE YOU A HAND HERE.
4^9=2^18 then the stem is equal to( 2^18)*5^25=10^18*5^7.
10^18 has 19 digits and 5^7 has 5 digits. Then the resulting number will have 5 digits from 5^7 and 18 zeros or N is 23
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good job BG. :cool



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Hi there,
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